2016 Update

Task/Semordnilap/C-sharp/semordnilap.cs

@@ -0,0 +1,39 @@
+using System;
+using System.Net;
+using System.Collections.Generic;
+using System.Linq;
+using System.IO;
+
+public class Semordnilap
+{
+    public static void Main() {
+        var results = FindSemordnilaps("http://www.puzzlers.org/pub/wordlists/unixdict.txt").ToList();
+        Console.WriteLine(results.Count);
+        var random = new Random();
+        Console.WriteLine("5 random results:");
+        foreach (string s in results.OrderBy(_ => random.Next()).Distinct().Take(5)) Console.WriteLine(s + " " + Reversed(s));
+    }
+
+    private static IEnumerable<string> FindSemordnilaps(string url) {
+        var found = new HashSet<string>();
+        foreach (string line in GetLines(url)) {
+            string reversed = Reversed(line);
+            //Not taking advantage of the fact the input file is sorted
+            if (line.CompareTo(reversed) != 0) {
+                if (found.Remove(reversed)) yield return reversed;
+                else found.Add(line);
+            }
+        }
+    }
+
+    private static IEnumerable<string> GetLines(string url) {
+        WebRequest request = WebRequest.Create(url);
+        using (var reader = new StreamReader(request.GetResponse().GetResponseStream(), true)) {
+            while (!reader.EndOfStream) {
+                yield return reader.ReadLine();
+            }
+        }
+    }
+
+    private static string Reversed(string value) => new string(value.Reverse().ToArray());
+}